1. Field of the Invention
The present invention relates to a brushless motor to be equipped in a disk drive for recording and reproducing or for simply reproducing information stored on an optical disk. In particular, the present invention relates to improvement in a rotor retaining mechanism in accordance with a thinned brushless motor.
2. Description of the Related Art
A personal computer mainly used as a portable device has been developed to become lighter and thinner for better portability. Accordingly, it is required to thin a disk drive to be equipped in the personal computer. Reduction in thickness can be achieved by adopting a slot-in disk drive for directly dragging a plate-shaped disk thereinto since this type of disk drive requires no tray for mounting a disk. Such improvement is not sufficient and there is still a demand for a further thinned personal computer. In order to fulfill such a demand, it is required to further thin a spindle motor (brushless motor) to be equipped in a disk drive, as well as to thin the disk drive itself to be equipped in the personal computer.
Improvement in a rotor retaining mechanism is one of objects to be achieved for obtaining a thinner brushless motor. There are, for example, two types of rotor retaining mechanisms such as a shaft retaining type and a hook-shaped type.
An entire structure of the brushless motor is described with reference to FIGS. 7 and 8. FIGS. 7 and 8 are schematic views respectively showing these two types of retaining mechanisms. Each of FIGS. 7 and 8 is a partial cross-sectional view of the brushless motor to be equipped in a disk drive. In these drawings, like parts are given like reference numerals.
The brushless motor includes a rotor 100 for allowing a disk-shaped storage medium (hereinafter, simply referred to as a storage disk) such as a CD (compact disc) to be removably mounted thereon, a bearing 101 for supporting the rotor 100 in a rotatable manner, a housing 102, and the like. The rotor 100 has a turntable 103 in a substantially disk shape for allowing a storage disk to be mounted on an upper surface thereof, a chucking device 104 incorporated in the upper surface of the turntable 103 and allowing the storage disk to be removable, a shaft 105 and a rotor magnet 106 respectively attached integrally to the turntable 103. The bearing 101 for supporting the shaft 105 in a rotatable manner is fixed in the housing 102 to be mounted to a mounting plate 107. On an opposite side of the housing 102 to the shaft 105, there is fixed a stator 108 facing the rotor magnet 106 with a space therebetween and generating a rotational magnetic field to rotary drive the rotor 100. A pressurizing magnet 109 is arranged between the turntable 103 and the housing 102. The turntable 103 can be stably rotated since the turntable 103 is attracted toward the housing 102 by magnetic force.
The rotor 100 is mounted onto the housing 102 and the like by, for example, inserting the shaft 105 into the bearing 101. The rotor retaining mechanism is provided for preventing the mounted rotor 100 from dropping off the bearing 101.
As shown in FIG. 7, an example of the rotor retaining mechanism of the shaft retaining type includes a groove 110 formed near a lower end of the shaft 105 of the rotor 100 over the entire circumferential length of the shaft 105, and a retaining member 113 fixed to the housing 102 with one end 111 thereof placed inside the groove 110. According to such a configuration, the end 111 of the retaining member 113 butts an inner bottom surface 114 of the groove 110 before the rotor 100 completely drops off due to upward movement of the shaft 105, thereby preventing the rotor 100 from dropping off.
FIG. 8 shows an example of the rotor retaining mechanism of the hook-shaped type. This rotor retaining mechanism includes a retaining member 121 attached onto a bottom surface of the turntable 103 of the rotor 100 with an elastic spring arm 120 having an end in a hook shape in cross section and projecting toward the housing 102, and an engaging portion 122 provided at one end of a tube portion of the housing 102 and engaged with the hook-shaped end of the retaining member 121. According to such a configuration, the spring arm 120 is elastically deformed if the hook-shaped end of the retaining member 121 and the engaging portion 122 come into contact with each other while the rotor 100 is mounted onto the housing 102 and the like. Moreover, if force which forces the rotor 100 to drop off is applied to the rotor 100 after the rotor 100 has been mounted onto the housing 102 and the like, the rotor 100 is prevented from dropping off since the hook-shaped end of the retaining member 121 and the engaging portion 122 butt with each other.